316 Transactions. — Botany. 



Cosmarium marr/aritifenim, Turpin. 



Figs. 27-29. 

 I give here three different forms which I beheve to be the same plant, 

 on account chiefly of their similar side view, which is elliptic in all three. 



The first (fig 27) is very much like Cosmarium broomeii, Thwaites, 

 (E. XVI.), and for a long time I believed it to be that plant. But C. 

 hroomeii has, in side view, a very distinct inflation at the middle, which my 

 plant has not. 



The second (fig. 28) resembles in outline C. pyramidatum, Brebisson, 

 but that species has a smooth instead of a pearly edge. Also, in its slightly 

 truncate ends, it approaches somewhat C. botrytis, Bory, (E. XVI.), but I 

 think it is much too large, and the pearly granules are rounder. Besides, 

 the truncation is often almost inconspicuous. 



The third (fig. 29) is the normal form of C. margaritiferum, occurring 

 here commonly. 



On the whole, I would set all three down as the same plant, though fig. 

 28 may be C. botrytis. 



Cosmarium- ralfsii, Brebisson. 



Fig. 30. 

 The figure shows the slight compression of the ends and thickening of 

 the inner surface of the cell-wall, neither of which has been noticed, I 

 think, elsewhere, but which I have observed here somewhat frequently. 

 When first seen I took them to be accidental, but have since seen many 

 examples. 



Staurastrum (avicula? ). 



Figs. 31, 32. 

 Had I obtained several specimens of this plant I should probably have 

 considered it as new from its crenate edges and double terminal s^Dines ; 

 but having only seen one I do not like to make sure of it. Ealfs (tab. 

 XXIII.) figures S. avicula with smooth edges and a single mucro. The 

 numerous species of Staurastrum are mostly very minute, and I think not 

 very clearly differentiated. 



Closterium acerosum, Schrank. 



Fig 33. 

 The figure shows the sigmoid form sometimes assumed here by this 

 plant, and alluded to above in the catalogue. 

 Closterium rostratiim, Ehrenberg. 



Fig. 34. 

 Closteriuvi setaceum, Ehrenberg. 



Fig. 35. 

 The figures are given to show the resemblance between the two plants. 



